Using a wooden spoon, a food mixer or an electric whisk, beat together the butter and sugars until just combined. Add the orange zest, then the egg, and beat in well.

Sift together the flour and bicarbonate of soda, then add to the mixture, stirring until it just comes together into a dough. Add the chocolate and cranberries, and chill in the fridge for 30 mins.

Preheat the oven to 180C. Line two baking trays with greaseproof paper, and divide the mixture into golf-ball sized rounds, spacing them well apart. Bake for about 15 minutes, until golden, but not browned.

Allow to cool on the tray for a couple of minutes, before moving to a wire rack to cool completely (or eat whilst still a little a bit warm).